1. Technical Field
The disclosure relates generally to charge damage evaluation of semiconductor-on-insulator (SOI) technology.
2. Background Art
One problem that exists when designing integrated circuits with silicon-over-insulator (SOI) transistors relates to detecting which SOI transistors may be susceptible to charging damage. Once detected, either design changes can be made or protection can be provided to those devices. In SOI it is impossible to “tie down” a floating gate in the traditional sense, such as by adding a diode connection to the substrate or nwell. SOI technologies are inherently less susceptible to charging damage because both the source/drain and the gate tend to have similar antennas, so the potential of both nodes varies together. This is not, however, certain in all cases.
Current treatment of SOI antennas involve examining the antennas attached to each transistor, one at a time, and calculating the allowable antenna area to determine potential for charge damage as if there were no additional or parallel current paths. An antenna is an amount of material on a net that is capable of carrying a charge. The charge carrying potential is measured by area of the antenna. Hence, the larger the area, the more charge that can be carried and the larger the likelihood of charge damage. Conventionally, each transistor not shunted by a net connection is evaluated to determine the antenna areas on the gate node and the source/drain node. For example, FIG. 1 shows a schematic diagram of an illustrative relationship between source/drain and gate antennas 10, 12 (may include either via(s) or metal wire(s) area) and a transistor 14 (shown as block for clarity). In this example, there is a source/drain (active region) antenna 10 connected to source and/or drain regions 16 of transistor 14 and a gate (polyconductor or metal) antenna 12 connected to a gate 18 of transistor 14, e.g., where polyconductor covers the active region. In this simple case, the area of source/drain and gate antennas 10 and 12 for each transistor 14 are determined and evaluated as to whether charging damage may occur. The above-described technique, however, takes a conservative approach to determine allowable antenna area in that the amount of gate insulator area that may exist between antennas 10, 12 is not considered in the above analysis.